The present invention is generally directed to ink compositions useful in various imaging systems, and more specifically, the present invention is directed to certain ink jet printing compositions, and to processes for the preparation thereof. Accordingly, in one embodiment of the present invention, there are provided aqueous ink compositions comprised of modified polyimines, especially specific derivatives of polyethyleneimines. The aforementioned ink compositions, in addition to possessing improved waterfastness, are thermally stable; are of a desirable nonfishy odor; and further, these inks are free of environmental hazards in that they, for example, generate negative Ames test properties, and thus are nonmutagenic. Also, the ink compositions of the present invention can be altered by adding thereto spreading substances such as benzyl alcohol, thereby enabling increased spot sizes. In addition, the ink compositions of the present invention also possess other desirable characteristics including low viscosity values; and further, these compositions are stable at elevated temperatures.
Compositions which are useful in ink jet printing systems are well known, and generally contain water soluble dyes. There is thus disclosed, for example, in U.S. Pat. No. 3,846,141 an ink composition useful in jet printing comprised of an aqueous solution of a water soluble dye, and a humectant material formed of a misture of a lower alkocy triglycol; and at least one other compound selected from the group consisting of a polyethylene glycol, a lower alkyl ether of diethylene glycol, and glycerol. According to the disclosure of this patent, the printing inks viscosity is subjected to little variation with use as water is lost by evaporation during recirculation of the ink composition through the jet printer. Moreover, apparently the humectant system disclosed in this patent substantially prevents or minimizes tip drying of the printing ink in the jet orifice or nozzle during down time of the printer, such as when the printer is rendered inoperative. As further disclosed in this patent, the basic imaging technique in jet printing involves the use of one or more ink jet assemblies connected to a pressurized source of ink. Each individual ink jet includes a very small orifice usually of a diameter of 0.0024 inches, which is energized by magneto restrictive piezo-electric means for the purpose of emitting a continuous stream of uniform droplets of ink at a rate of 33 to 75 kilohertz. This stream of droplets is desirably directed onto the surface of a moving web of, for example paper, and is controlled to form printed characters in response to video signals derived from an electronic character generator and in response to an electrostatic deflection system.
Also, there is disclosed in U.S. Pat. No. 4,279,653 ink jet compositions containing water-soluble wetting agents, a water-soluble dye and an oxygen absorber. Similarly, U.S. Pat. No. 4,196,007 describes an ink jet printing composition containing an aqueous solution of a water-soluble dye and a humectant consisting of at least one water-soluble unsaturated compound. Further, there is disclosed in U.S. Pat. No. 4,267,088 coatings particularly useful as marking inks wherein there is selected an epichlorohydrin - modified polyethyleneimine, and an ethylene oxide modified polyethyleneimine in an aqueous solution. Other patents of interest are U.S. Pat. Nos. 4,101,329; 4,290,072; 4,383,859; 4,235,773; 4,279,814; 4,443,371; 4,286,989; 4,299,630; 4,167,393; 3,864,296; 4,238,234; 3,234,025; 4,520,143; 3,920,855 and 4,182,612.
Additionally, there are disclosed in U.S. Pat. No. 4,197,135 ink compositions with improved waterfastness comprised of at least one water soluble dye, and a polyamine with 7 or more nitrogen atoms per molecule. Specifically, there is illustrated in this patent an ink composition comprising an aqueous solution of at least one water-soluble dye, and from about 0.5 percent to about 10 percent by weight of a polyamine having 7 or more nitrogen atoms per molecule; and wherein the composition has a pH of 8 or above. In column 1, beginning at line 61, it is indicated that the preferred polyamines have the hydrogen of the primary amine group replaced with either a methyl or a hydroxyethyl group. Examples of fully substituted polyamines selected are outlined in column 2, beginning at line 40, of the U.S. Pat. No. 4,197,135. The invention of the present application is directed to similar inks with the primary exceptions that the amine, and more specifically, the polyethylene amine or polyethyleneimine selected is of a lower molecular weight; and moreover the inks of the present invention are of a lower viscosity thereby providing for superior drop formation.
Furthermore, there is illustrated in U.S. Pat. No. 4,659,382, the disclosure of which is totally incorporated herein by reference, an ink composition with improved waterfastness useful for jet printing processes comprised of a major amount of water, a hydroxyethylated polyethyleneimine polymer, and a dye composition wherein the polymer has incorporated therein from about 65 percent to about 80 percent by weight of hydroxyethyl groups. A specific preferred ink composition illustrated in the aforementioned patent is comprised of from about 70 percent by weight to about 90 percent by weight of water; from about 1 percent by weight to about 10 percent by weight of a dye molecule; from about 2 percent by weight to about 6 percent by weight of a hydroxyethylated polyethyleneimine having incorporated therein from about 65 percent by weight to about 80 percent by weight of hydroxyl substituents; and additive components. The ink compositions of the present invention contain similar components as detailed in the aforementioned patent with the primary exceptions that there are selected for the inks of the present invention hydroxypropylated polyethyleneimines with specific molecular weights and specific viscosities.
Ink compositions for jet printing including those of the present invention can be prepared by a number of known methods. Generally, these methods involve dissolving the various dyes, humectants, viscosity control agents, paper fixing additives, surface tension control additives, biocides, polyimine and anti-oxidants in a known volume of water, followed by adjusting the pH of the solution to desirable level. In those situations where the pigments selected are not water-soluble, the inks are prepared by standard known milling processes. However, the latter pigment dispersions are generally not sufficiently stable, accordingly when incorporated into a printing machine the ink particles tend to agglomerate resulting in the clogging of the small nozzles contained in the ink jet devices.
While the above compositions may be suitable for their intended purposes, there continues to be a need for improved jet ink compositions and processes thereof. Additionally, there continues to be a need for ink jet compositions which when in use result in superior optical print densities, and have excellent waterfastness characteristics. Moreover, there continues to be a need for inks that possess nonmutagenic characteristics enabling them to be safey used in ink jet printing processes. Also, there is a need for ink compositions that enable an increase in the spot size of the ink. Furthermore, there is a need for nonmutagenic ink compositions with acceptable waterfastness characteristics, and a viscosity of from about 1 centipoise to about 5 centipoise, which inks are also thermally stable.